Real-time stealth optical transmission via dither-remodulation in a bias controller of a Mach-Zehnder modulator.

The physical layer transmission security is a promising technology against security threats. As an effective supplement to the encryption strategy, steganography has received widespread attention. We report a real-time 2 kbps stealth transmission in the 10 Gbps dual polarization QPSK public optical communication. The stealth data is embedded in dither signals via precise and stable bias control technique for a Mach-Zehnder modulator. In the receiver, the stealth data can be recovered from the normal transmission signals by low SNR signal processing and digital down conversion. The stealth transmission has been verified to pose almost no impact on the public channel over a 117 km distance. The proposed scheme is compatible with existing optical transmission systems, so that no new hardware needs to be employed. It can be accomplished and is exceeded economically by adding simple algorithms, which utilizes only a small amount of FPGA resources. The proposed method can cooperate with encryption strategies or cryptographic protocols at different network layers to reduce the communication overhead and improve the overall security of the system.